This summer I returned home to California for a month. With all my planning to travel safely during a health pandemic, what I didn’t count on was the onset of early season fires caused by an unusual lightning event following days of extremely high temperatures. I had planned to stay in isolation for 14 days after my flight, but I hadn’t planned to stay fully inside the whole time. However, the heat wave and then even more importantly, the smoky air quality made going outside very difficult.

After a few days, friends alerted me to PurpleAir (https://www2.purpleair.com/), a network of citizen-installed air quality sensors strategically located throughout the region that supplement the official network of sensors. Since the nearest official sensor is 12 miles away, and the region is hilly and filled with microclimate variations, I discovered the local sensors are a much more accurate gauge of the local air quality. Often I found huge discrepancies between what I was experiencing and what was indicated on the official weather site.

For example, as I am writing this, here is the situation: The official AirNow gage (https://www.airnow.gov) shows the following air quality levels, with a reading of 158 PM AQI PM2.5^*:

My local neighbourhood monitors shown on the Purple Air site are currently showing above 200 AQI. About an hour ago, the skies had cleared here and we actually dropped down in the low 100s for a bit, and that never showed in the regional sensor. Just that short dip in bad air quality meant that I could go outside for a quick walk.

The daily routine here now is to consult Purple Air and fire maps alongside regular daily and hourly temperature apps. Thankfully, the citizen sensor networks are available and linked together to provide brilliant real-time information for those of us whose daily activities need to be guided by this information.

* US EPA PM2.5 AQI An air quality index (AQI) is a number used by government agencies to communicate to the public how polluted the air currently is or how polluted it is forecast to become. EPA uses two algorithms, called “NowCasts,” to relate hourly readings from air quality monitors to the AQI for ozone and the AQI for particle pollution. There is a separate algorithm for each.